1. Field of the Invention
The present invention relates to granules of .alpha.-L-aspartyl-L-phenylalanine methyl ester (.alpha.-APM) having improved water-solubility. The granules of the present invention may be packaged to protect the granules from destruction or damage during transportation or storage and to allow direct use of the granules as a sweetener.
2. Discussion of the Background
.alpha.-APM is a dipeptide sweetener having a sweetness of about 200 times that of sucrose (cane sugar). Because of its extreme sweeteners and the low calory content, it is widely used as a diet sweetener, and the worldwide demand for it is estimated to be over 10,000 tons by 1995.
Since .alpha.-APM is an added sweetener which has little bitterness or bad aftertaste, in contrast to other high-sweetness sweeteners, it is widely used and popularized as a low-calory sweetener. However, one drawback is often pointed out, i.e., that the dispersibility and solubility in water is poor. Therefore, in order to obtain .alpha.-APM having excellent solubility, various investigations for granulating or foaming and tableting it have been made by adding a vehicle or disintegrator thereto.
However, incorporation of a vehicle into .alpha.-APM is often problematic for particular uses. Therefore, high-purity and high-solubility .alpha.-APM is greatly desired.
As an attempt to improve the solubility of .alpha.-APM while maintaining high purity, a method of spray-drying a slurry of .alpha.-APM is known (Japanese Patent Publication 58-20558). A method of granulating .alpha.-APM, to which water has been added to a specified water content is also known (Japanese Patent Application Laid-Open No. 59-95862).
On the other hand, processes for producing .alpha.-APM crystals are known to produce various crystal forms (European Patent 0119837). Of these crystal forms, IB crystals have a higher solubility than IIA crystals and IIB crystals, as dry crystals.
However, IB form crystals of .alpha.-APM are known to still contain crystals having low solubility. For example, crystal characteristics, i.e., whether bundle-like crystals form or needle-like crystals form, causes noticeable differences in the dispersibility and solubility of crystals in water. The bundle-like crystals have a higher dispersibility and solubility in water than the needle-like crystals.
IB needle-like crystals often require a long time for dispersing or dissolving them into water, which is almost comparable to IIA crystals or IIB crystals, depending upon the crystallization and drying conditions employed in preparing them.
The term "needle-like crystals", as referred to herein, indicate those crystals which are obtained by cooling crystallization under ordinary stirring conditions without a pseudo-solid phase.
The term "bundle-like crystals", as referred to herein with respect to crystal behavior, indicate those crystals which are obtained by cooling crystallization of an .alpha.-APM solution with no stirring condition via its pseudo-solid phase, as described in Japanese Patent Publication No. 2-45638 (crystallization of .alpha.-APM). When these crystals are observed with a scanning electron microscope (SEM) under magnification, they are found to be crystal aggregates where a plurality of needle-like crystals are bundled together to seemingly form one crystal.